Left atrial tachyarrhythmia in fetal lambs

To evaluate the hemodynamic effect of rapid left atrial pacing on fetal circulation, a fetal supraventricular tachyarrhythmia model was made and the aortic pressure, central venous pressure, and left and right ventricular outputs were measured in ten fetal lambs. Under maternal anesthesia, the uterus was opened, and under local anesthesia, catheters were inserted into thefetal superior vena cava and ascending aorta through a neck incision. Pacing leads were then sutured onto the fetal left atrial appendage via left thoracotomy. Ventricular output was estimated using echocardiography by a transuterine approach. Fetal hemodynamics were observed without pacing (control), and at the pacing rates of 200, 300, 350, and 400/min. The aortic pressure decreased when the left atrium was paced at 300/min or more and the central venous pressure increased when the left atrium was paced at 350/min or more. The left and right ventricular outputs decreased when the left atrium was paced at 350/min or more. The left ventricular output was 215+/-54 mL/kg per minute at control, 205+/-60 mL/kg minute when paced at 200/min, 178+/-58 mL/kg per minute when paced at 300/min, but decreased to 164+/-44 mL/kg per minute when paced at 350/min and to 149+/-57 mL/kg per minute when paced at 400/min. The right ventricular output was 338+/-66 mL/kg per minute at control, 336+/-95 mL/kg per minute when paced at 200/min, 273+/-91 mL/kg per minute when paced at 300/min, but decreased to 256+/-80 mL/kg per minute when paced at 350/min and to 202+/-76 mL/kg per minute when paced at 400/min. Fetal circulatory failure was initially confirmed when the left atrium was paced at 300/min in this left atrial tachyarrhythmia model.